The personality development of young children, on whom there is both genetic and rearing information, is investigated. The children are of normal parents and of depressed parents. Affective, social, and cognitive aspects of behaviors are examined. Children, initial ages 15- to 24-months and their siblings (5- to 8-years) are studies over a 3-year period. The several criteria guiding the selection of variables are: (a) critical developments in the transition from infancy to early childhood, and in the early school years, (b) interrelations of affective, social, and cognitive development, and (c) qualities presumed to be at risk in children of affectively ill parents. Personality is investigated relative to (a) the child's responsiveness to stimulation in the environment--new, pleasurable, and confrontational or aversive stimulation, (b) qualities of the child's affect and affect regulation, (c) qualities of the child's relationships, and (d) the child's sense of self. Work is progressing on conceptual and measurement issues.